http://www.bmeengine.com/engines.htm
Picture of the sport 50 shows an external pulse line to the pump. Walbro carbs have a thickened area in the pump cover to drill and tap for an external pulse line. You can remove the carb and it's pump cover to see where to place a nipple centered over the pump diaphram. Typicaly the pulse line runs through the carb base and gasket as well as through the carb. That makes for a long path for the pulse to run to opperate the pump. The external line makes for a clearer path. Looking at the BME engines I see they all have external pulse lines now.